Film coating apparatus and method



y 5, 1964 F. CHARLES-MESSANCE 7 3, 3

FILM COATING APPARATUS AND METHOD Filed April 19, 1961 FIG. PRIOR ART Inventor Fl'hugou. (Map l- 5 $4"; and;

Attorney l j t United States Patent .0

3,132,040 FILM COATING APPARATUS AND METHOD Frangois Charles-Messance, Paris, France, assignor t Cellophane Investment Company Limited, Alderney, Channel Islands, a corporation Filed Apr. 19, 1961, Ser. No. 104,160 Claims priority, application France Apr. 22, 1960 Claims. (Cl. 117-68) This invention relates to the application of coatings to both sides of a continuous web of film base. It will be described with reference to the accompanying drawings, to which more detailed reference is made later herein.

In French Patent No. 997,734 a method of coating film base successively on both faces, particularly with aqueous dispersions of certain resins, has been described.

FIGURE 1 illustrates the basic apparatus of the prior art and is referred to below;

FIGURE 2 illustrates a first form of apparatus accord ing to this invention;

FIGURE 3 illustrates a second form of apparatus accor-ding to this invention; and

FIGURE 4 illustrates a third form of apparatus according to this invention.

The principle of the method and an apparatus for carrying it out are illustrated in FIGURE 1 of the accompanying drawings. Thus, referring to FIGURE 1:

A continuous web of film to be coated, for example a film of regenerated cellulose, is unwound from a roll 1 and fed through the nip of juxtaposed horizontal rolls 2 and 3. The two rolls turn in the directions shown by the arrows. These two rolls define between them a trough 5 into which there is fed an aqueous dispersion of a copolymer resin. The dispersion wets the film and the water is progressively absorbed, thus leaving a deposit Of copolymer particles.

The film leaving the nip between the rolls travels a further distance around the roll 2 and thereafter passes, via guide rollers 6 and 8, through a drier 7. During the drying step the particles of resin coalesce and form a uniform coating on one face of the film.

The film then passes over another guide roller 9, and it is directed back to the nip between the rolls 2 and 3. By thus through the nip a second time the second face of the film receives a coating. On leaving the nip between rolls 2 and 3 for a second time, the film is guided, via guide rollers 10 and 12, through a drier 11, thus forming a uniform coating on the second face. The dry film, coated on both faces, is finally re-wound at 13.

The method, while being very advantageous, has the disadvantage that the coating of the resin dispersion is often non-uniform, i.e. on separation of the lengths of film leaving the nip between the rolls 2 and 3, the coatings are found to be striated, a condition which is more readily seen if the coating composition is coloured. This defect, which is sometimes called streaking, may be lessened by certain additions to the dispersion, or by mechanically 0r pneumatically scraping or smoothing the coatings on the delivery side of the nip between the rolls 2 and 3. It is, however, difiicult by such means to eliminate the defect entirely.

It will be noted from FIGURE 1 of the drawings that the two juxtaposed film webs pass through the nip together and are separated one from the other immediately as they leave the nip between the rolls. It has now been found that the defect referred to above may be substantially minimized by delaying to a stage beyond the nip the point of separation of the film webs.

According to a first feature of the present invention there is provided a process for applying a coating composition, consisting of an aqueous dispersion of a polymer or copolymer resin, to both sides of a continuous web of film which comprises causing the web to pass through the nip of a pair of horizontally disposed applicator rolls, guiding the web so that it returns to pass again through the said nip in the same direction therethrough but with that face of the film which was remote from one roll during said first pass being in contact with the other roll during said second pass, applying a coating composition simultaneously to the juxtaposed faces of the web as it passes through the said nip, and subjecting the web to a continuous drying operation between its first and second pass through the said nip and after it has passed through the said nip a second time, the juxtaposed areas of the web passing through the nip being maintained in contact for a distance beyond the exit side of thenip.

When the separation of the two areas of film web is not retarded a thick liquid mensicus forms at the point of their separation. The more the point of separation is retarded, the more is the thickness of the meniscus reduced and the more the striations disappear. However, the separation must not be retarded beyond a certain limit because otherwise :the meniscus disappears completely, the coating dries to too great an extent and the separation takes place unsatisfactorily with formation of opaque areas. The minimum distance of the point of separation from the nip necessary to give usefully improved results increases with the coating speed, i.e. the peripheral speed of the rolls 2 and 3, and it also varies with the properties of the dispersion. Generally, for example with a coating speed of 30 metres per minute, the minimum distance for satisfactory results is about millimetres.

According to a further feature of the invention, there is provided apparatus for applying a coating composition to both sides of a continuous web of film, which comprises a pair of horizontally disposed applicator rolls defining a nip between them, means for causing a web of film to traverse first through the said nip and for guiding the web through the same nip a second time in the same direction therethrough, said guiding means being constructed and arranged so that the face of the web which was remote from one applicator roll during the first passage of the web through the nip is in contact with the other applicator roll during the second passage of the web through the nip, means for supplying a coating composition to the said nip so that it is applied to the juxtaposed faces of the web as it passes through the nip, means for drying the web en route from its first pass to its second pass through the nip, and for drying the web a second time after its second pass through the nip, and means for constraining the juxtaposed areas of the web together for a distance beyond the exit side of the nip.

In the three FIGURES 2, 3 and 4, the references 2 and 3 correspond to the two rolls of FIGURE 1. The path followed by the lengths of film is indicated by arrows. A constantly replenished supply 5 of resin dispersion is contained in the dihedral between the convergent lengths of film. It will be understood that the complete apparatus in each case is that of FIGURE 1, modified by the ancillary members shown in FIGURES 2, 3 and 4, respectively.

Referring to FIGURE 2, the two lengths of film are adherent when they leave the gap between the rolls and remain adherent over the distance d. They then diverge towards the guide rollers 14, 15. The length which passes over roller 14 undergoes drying at 7 and thereafter a further coating at the nip between rolls 2 and 3. It then passes over guide roll 15 and is dried at 11 and rewound at 13.

Referring to FIGURE 3, the two lengths of film remain adherent until they pass between a pair of small presser rollers 16, 17, and separate on leaving the gap between those rollers. These two embodiments are substantially equivalent in effect.

Referring to FIGURE 4, the two lengths of film remain adherent while travelling along an arcuate path around the roll 2 and one length is then diverted around the guide roller 18. w v

What is claimed is:

1. A process for applying a coating composition consisting of an aqueous dispersion of a polymer or copolymer resinto both sides of a continuous web of film, which comprises causing the web to pass through the nip of a pair of horizontally disposed applicator rolls, guiding the Web so that it returns to pass again through the said nip in the same direction, but with that face of the film which was remote from one roll during said first pass being in contact with the other roll during said second pass, applying a coating composition simultaneously to the juxtaposed faces of the Web as it passes through the said nip, and subjecting the web to a continuous drying operation between its first and second pass through the said nip and after it has passed through the said nip a second time, the juxtaposed areas of the web passing through the nip being maintained in contact for a substantial distance beyond the exit side of the nip prior to the separation of the webs, said distance being not greater than that at which the meniscus of liquid which otherwise forms between the juxtaposed areas of the web at the exit side of the nip completely disappears whereby the coating material is split at the point of separation and forms a continuous coating on both of said webs.

2. A process according to claim 1, wherein the peripheral speed of the applicator rolls is about 30 metres per minute and the said distance over which the juxtaposed areas of the web are maintained in contact is about 100 millimetres.

Oswin, Nov. 18, 1952 Staehle Sept. 18, 1956 

1. A PROCESS FOR APPLYING A COATING COMPOSITION CONSISTING OF AN AQUEOUS DISPERSION OF A POLYMER OR COPOLYMER RESIN TO BOTH SIDES OF A CONTINUOUS WEB OF FILM, WHICH COMPRISES CAUSING THE WEB TO PASS THROUGH THE NIP OF A PAIR OF HORIZONTALLY DISPOSED APPLICATOR ROLLS, GUIDING THE WEB SO THAT IT RETURNS TO PASS AGAIN THROUGH THE SAID NIP IN THE SAME DIRECTION, BUT WITH THAT FACE OF THE FILM WHICH WAS REMOTE FROM ONE ROLL DURING SAID FIRST PASS BEING IN CONTACT WITH THE OTHER ROLL DURING SAID SECOND PASS, APPLYING A COATING COMPOSITION SIMULTANEOUSLY TO THE JUXTAPOSED FACES OF THE WEB AS IT PASSES THROUGH THE SAID NIP, AND SUBJECTING THE WEB TO A CONTINUOUS DRYING OPERATION BETWEEN ITS FIRST AND SECOND PASS THROUGH THE SAID NIP AND AFTER IT HAS PASSED THROUGH THE SAID NIP A SECOND TIME, THE JUXTAPOSED AREAS OF THE WEB PASSING THROUGH THE NIP BEING MAINTAINED IN CONTACT FOR A SUBSTANTIAL DISTANCE BEYOND THE EXIT SIDE OF THE NIP PRIOR TO THE SEPARATION OF THE WEBS, SAID DISTANCE BEING NOT GREATER THAN THAT AT WHICH THE MENISCUS OF LIQUID WHICH OTHERWISE FORMS BETWEEN THE JUXTAPOSED AREAS OF THE WEB AT THE EXIT SIDE OF THE NIP COMPLETELY DISAPPEARS WHEREBY THE COATING MATERIAL IS SPLIT AT THE POINT OF SEPARATION AND FORMS A CONTINUOUS COATING ON BOTH OF SAID WEBS. 